The present invention relates to a thermoplastic film that can be used to make packages for a wide variety of food and non-food products.
Vertical form/fill/seal (VFFS) packaging systems have proven to be very useful in packaging a wide variety of flowable products. An example of such systems is the Onpack(trademark) flowable food packaging system sold by W. R. Grace and Co.-Conn. through its Grace Packaging group. The VFFS process is known to those of skill in the art, and described for example in U.S. Pat. No. 4,589,247 (Tsuruta et al), incorporated herein by reference. A flowable product is introduced through a central, vertical fill tube to a formed tubular film having been sealed transversely at its lower end, and longitudinally. The pouch is then completed by sealing the upper end of the tubular segment, and severing the pouch from the tubular film above it.
The choice of packaging materials is important, and should be matched to the intended end use of the pouch.
Several properties are often desirable in such pouches.
Dimensional stability is of great importance in VFFS systems. In such systems, the equipment fills a pouch to a certain level. If the film stretches, too much product is put into the pouch. This phenomenon makes it difficult to standardize pouch dimensions, which leads for example to difficulty in packing off of pouches in shipping boxes of pre-determined size.
Sometimes a pouch material is used to package a product, such as an aqueous liquid food product, at an elevated temperature of 170 to 210xc2x0 F. This is known as a hot fill process. Sometimes the pouch, after filling, is exposed to retort conditions. In either case, the dimensional stability of the package is severely tested, and the possibility of package distortion increases.
The package material is preferably stiff (i.e. has a high modulus), especially at high temperatures. This is often necessary because the film tracks more easily on a packaging machine. Also, a hot fin seal can stretch undesirably; therefore, to preserve seal integrity, the ability to package at high speeds is limited by the degree to which hot seals will elongate or stretch. If a heavy load, e.g. 5 to 20 pounds of shredded cheese, is thrust into a pouch with transverse seals just formed, these seals are still hot and the pouch, or the seal area of the pouch, can deform. More uniform package length is related to more uniform package weight, which is important to the food processor in order to provide packages with consistent weights.
Good tensile strength is necessary in films used for such applications. Where flowable foods are packaged, as in many VFFS applications, the hydrostatic pressure of many oil and water based foods requires a tough, impact and abuse resistant packaging material that will maintain its structural integrity during the packaging process, and subsequent distribution and storage.
For hot fill and retort applications, heat resistance is essential to avoid package distortion or degradation of the film itself, or of the transverse and longitudinal seals associated with the VFFS process.
Oxygen barrier properties are also essential in end-uses where the product is susceptible to oxidative degradation.
Depending on the packaging process, form of the package, and nature of the product, physical properties such as barrier to ultraviolet light, surface printability, clarity, flatness, thermoformability, and low tear initiation and propagation (for easy-open packages) may become significant.
The inventors have found that a combination of many of these properties is possible through the use of at least one layer consisting essentially of amorphous polyamide in a multilayer thermoplastic film.
In a first aspect, a multilayer film comprises a core layer consisting essentially of an amorphous polyamide; two intermediate layers, disposed on opposite surfaces of the core layer, comprising a semicrystalline polyamide; two adhesive layers, each disposed on a surface of the respective intermediate layer, comprising a polymeric adhesive; and two outer layers, each disposed on a surface of a respective adhesive layer, comprising a material selected from the group consisting of amorphous polyamide, semicrystalline polyamide, ethylene/alpha olefin copolymer, propylene homopolymer, and propylene/alpha olefin copolymer.
In a second aspect, a multilayer film comprises a core layer comprising an amorphous polyamide adhesive; two intermediate layers, disposed on opposite surfaces of the core layer, consisting essentially of an amorphous polyamide; two adhesive layers, each disposed on a surface of the respective intermediate layer, comprising a polymeric adhesive; and two outer layers, each disposed on a surface of the respective adhesive layer, comprising a material selected from the group consisting of amorphous polyamide, semicrystalline polyamide, ethylene/alpha olefin copolymer, propylene homopolymer, and propylene/alpha olefin copolymer.
In a third aspect, a method of packaging a food product comprises providing a rollstock film, the film comprising a core layer consisting essentially of an amorphous polyamide; two intermediate layers, disposed on opposite surfaces of the core layer, comprising a semicrystalline polyamide; two adhesive layers, each disposed on a surface of the respective intermediate layer, comprising a polymeric adhesive; and two outer layers, each disposed on a surface of a respective adhesive layer, comprising a material selected from the group consisting of amorphous polyamide, semicrystalline polyamide, ethylene/alpha olefin copolymer, propylene homopolymer, and propylene/alpha olefin copolymer; forming the film into a tube in a vertical/form/fill/seal process; filling the tube with a food product; and closing the tube to form a sealed pouch containing the food product.
In a fourth aspect, a package comprises a flowable food product; and a pouch containing the food product, the pouch made from a film comprising a core layer consisting essentially of an amorphous polyamide; two intermediate layers, disposed on opposite surfaces of the core layer, comprising a semicrystalline polyamide; two adhesive layers, each disposed on a surface of the respective intermediate layer, comprising a polymeric adhesive; and two outer layers, each disposed on a surface of a respective adhesive layer, comprising a material selected from the group consisting of amorphous polyamide, semicrystalline polyamide, ethylene/alpha olefin copolymer, propylene homopolymer, and propylene/alpha olefin copolymer.
In a fifth aspect, a method of packaging a food product comprises providing a rollstock film, the film comprising a core layer comprising an amorphous polyamide adhesive; two intermediate layers, disposed on opposite surfaces of the core layer, consisting essentially of an amorphous polyamide; two adhesive layers, each disposed on a surface of the respective intermediate layer, comprising a polymeric adhesive; and two outer layers, each disposed on a surface of the respective adhesive layer, comprising a material selected from the group consisting of amorphous polyamide, semicrystalline polyamide, ethylene/alpha olefin copolymer, propylene homopolymer, and propylene/alpha olefin copolymer; forming the film into a tube in a vertical/form/fill/seal process; filling the tube with a food product; and closing the tube to form a sealed pouch containing the food product.
In a sixth aspect, a package comprises a flowable food product; and a pouch containing the food product, the pouch made from a film comprising a core layer comprising an amorphous polyamide adhesive; two intermediate layers, disposed on opposite surfaces of the core layer, consisting essentially of an amorphous polyamide; two adhesive layers, each disposed on a surface of the respective intermediate layer, comprising a polymeric adhesive; and two outer layers, each disposed on a surface of the respective adhesive layer, comprising a material selected from the group consisting of amorphous polyamide, semicrystalline polyamide, ethylene/alpha olefin copolymer, propylene homopolymer, and propylene/alpha olefin copolymer; forming the film into a tube in a vertical/form/fill/seal process; filling the tube with a food product; and closing the tube to form a sealed pouch containing the food product.
Definitions
xe2x80x9cAdhesivexe2x80x9d herein refers to polymeric adhesive, more preferably an olefin polymer or copolymer having an anhydride functionality grafted thereon and/or copolymerized therewith and/or blended therewith.
xe2x80x9cAmorphous polyamidexe2x80x9d herein refers to those polyamides which are lacking in crystallinity as shown by the lack of an endotherm crystalline melting peak in a Differential Scanning Calorimeter (DSC) test (ASTM D-3417). Examples of such polyamides include those amorphous polymers prepared from the following diamines: hexamethylenediamine, 2-methylpentamethylenediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4- trimethylhexamethylenediamine, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)isopropylidine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, meta-xylylenediamine, 1,5-diaminopentane, 1,4-diaminobutane, 1,3-diaminopropane, 2-ethyldiaminobutane, 1,4-diaminomethylcyclohexane, p-xylylenediamine, m-phenylenediamine, p-phenylenediamine, and alkyl substituted m-phenylenediamine and p-phenylenediamine. Examples of polyamides that can be used include those amorphous polymers prepared from the following dicarboxylic acids: isophthalic acid, terephthalic acid, alkyl substituted iso- and ter-ephthalic acid, adipic acid, sebacic acid, butane dicarboxylic acid, and the like. The diamines and diacids mentioned above can be combined as desired, provided the resulting polyamide is amorphous. That is, an aliphatic diamine can generally be combined with an aromatic diacid, or an aromatic diamine can generally be combined with an aliphatic diacid to give suitable amorphous polyamides. Preferred amorphous polyamides are those in which either the diamine or the diacid moiety is aromatic, and the other moiety is aliphatic. The aliphatic groups of these polyamidesides preferably contain between 4 and 12 carbon atoms in a chain or an aliphatic cyclic ring system having up to 15 carbon atoms. The aromatic groups of the polyamides preferably have mono or bicyclic aromatic rings which may contain aliphatic substituents of up to about 6 carbon atoms.
xe2x80x9cAmorphous polyamide adhesivexe2x80x9d herein refers to those polymeric materials which bond a layer of amorphous polyamide to a layer comprising another polymer or blend of polymers. Preferred polymeric materials include semicrystalline polyamide; anhydride grafted polymers such as anhydride grafted ethylene/1-butene copolymer, anhydride grafted ethylene/1-hexene copolymer, and anhydride grafted ethylene/1-octene copolymer; ethylene/acrylic acid copolymer; and ethylene/methacrylic acid copolymer.
xe2x80x9cAnhydride functionalityxe2x80x9d herein refers to any form of an hydride functionality, such as the anhydride of maleic acid, fumaric acid, etc., whether grafted onto a polymer, copolymerized with a polymer, or blended with one or more polymers, and is also inclusive of derivatives of such functionalities, such as acids, esters, and metal salts derived therefrom.
xe2x80x9cCore layerxe2x80x9d herein refers to the central layer of a multi-layer film.
xe2x80x9cEthylene/alpha-olefin copolymerxe2x80x9d (EAO) herein refers to copolymers of ethylene with one or more comonomers selected from C4 to C10 alpha-olefins such as butene-1 (i.e., 1-butene), hexene-1, octene-1, etc. in which the molecules of the copolymers comprise long chains with relatively few side chain branches or cross-linked structures. This molecular structure is to be contrasted with conventional low or medium density polyethylenes which are more highly branched than their respective counterparts. EAO includes such heterogeneous materials as linear medium density polyethylene (LMDPE), linear low density polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE and ULDPE); as well as homogeneous polymers (HEAO) such as TAFMER(trademark) ethylene/alpha olefin copolymers supplied by Mitsui Petrochemical Corporation and metallocene-catalyzed polymers such as EXACT(trademark) resins supplied by Exxon and AFFINITY(trademark) resins supplied by the Dow Chemical Company. EAO includes long chain branched homogeneous ethylene/alpha-olefin copolymer. An EAO can for example, have a density of between 0.916 and 0.945 grams/cc.
xe2x80x9cEthylene/vinyl ester copolymerxe2x80x9d (E/VE) herein refers to a copolymer derived from ethylene and an ester such as vinyl acetate, alkyl acrylate, methyl methacrylate, or other monomers, wherein the ethylene derived units in the copolymer are present in major amounts and the ester derived units in the copolymer are present in minor amounts.
xe2x80x9cFlowable materialsxe2x80x9d herein means food or non-food items which are flowable under gravity, or can be pumped, as defined in U.S. Pat. No. 4,521,437 (Storms), incorporated by reference herein in its entirety.
xe2x80x9cHeat shrinkablexe2x80x9d herein is a property of a material which, when heated to an appropriate temperature above room temperature (for example 96xc2x0 C.), will have a free shrink of 5% or greater in at least one linear direction.
xe2x80x9cHigh density polyethylenexe2x80x9d (HDPE) herein has a density of 0.94 grams per cubic centimeter to 0.96 grams per cubic centimeter.
xe2x80x9cIntermediatexe2x80x9d herein refers to a layer of a multi-layer film which is between an outer layer and core layer of the film.
xe2x80x9cLinear low density polyethylenexe2x80x9d (LLDPE) herein has a density in the range of from 0.916 to 0.925 grams per cubic centimeter.
xe2x80x9cLinear medium density polyethylenexe2x80x9d (LMDPE) herein has a density from 0.926 grams per cubic centimeter to 0.939 grams per cubic centimeter.
xe2x80x9cOuter layerxe2x80x9d herein refers to what is typically an outermost, usually surface layer of a multi-layer film, although additional layers and/or films can be adhered to it.
xe2x80x9cPolyamidexe2x80x9d herein refers to both polyamides and copolyamides, and means a polymer in which amide linkages (xe2x80x94CONHxe2x80x94) occur along the molecular chain. Examples are nylon 6, nylon 11, nylon 12, nylon 66, nylon 69, nylon 610, nylon 612, nylon 6/66, and amorphous polyamide.
xe2x80x9cPolymerxe2x80x9d herein refers to homopolymer, copolymer, terpolymer, etc. xe2x80x9cCopolymerxe2x80x9d herein includes copolymer, terpolymer, etc.
xe2x80x9cPropylene/alpha-olefin copolymerxe2x80x9d herein refers to copolymers of propylene with one or more comonomers selected from ethylene, and butene-1 (i.e., 1-butene).
xe2x80x9cSemicrystalline polyamidexe2x80x9d herein refers to polyamides having readily determined crystalline melting points, for example, nylon 6, 9, 11, and 12. Such nylons may also have amorphous regions, and may even have measurable glass transition temperatures.
All compositional percentages used herein are calculated on a xe2x80x9cby weightxe2x80x9d basis.
xe2x80x9cLDxe2x80x9d or xe2x80x9cMDxe2x80x9d herein refers to longitudinal direction or machine direction respectively, synonymous terms for the direction of the film parallel to the path of extrusion. xe2x80x9cTDxe2x80x9d or xe2x80x9cCDxe2x80x9d herein refers to transverse or cross direction respectively, synonymous terms for the direction of the film transverse to the path of extrusion.